STRETCH-ACTIVATED CHANNELS IN AIRWAY EPITHELIAL-CELLS

Two types of stretch-activated (SA) ion channels were identified in the basolateral membrane of isolated rabbit airway epithelial cells by patch-clamp techniques. Pressure activation and deactivation of one channel, which had a conductance of 29 pS, occurred after a delay of approximately 20-30 s. The open probability of this delayed stretch-activated (DSA) channel was increased from <0.01 to 0.45 at 50 mmHg of suction. The reversal potential of the DSA channel, calculated from the pipette potential at which membrane currents reversed [-31.3 +/- 3.6 (SD) mV] and the resting membrane potential (-27.8 +/- 3.3 mV) was +3.5 +/- 3.3 mV. None of the equilibrium potentials of the ions used were similar to the calculated reversal potential of the DSA channel, suggesting that this channel is nonselective for cations. The DSA channel gating behavior was characterized by bursts of rapid transitions between open and closed states. The distribution of the open and closed times revealed that this gating behavior could be fitted with two open states and two closed states. Only the slow time constant of the closed state was decreased by suction. The second SA channel was selective for K+ and had a conductance of 65 pS but a long delay was not associated with the pressure sensitivity of this channel. The open probability of the K+-selective SA channel was increased from <0.01 to 0.30 by 50 mmHg of suction. The K+-selective SA channel was distinct from the well-characterized basolateral K+ channel.